Photonic crystal microspheres built up by mono-dispersed particles have been known to yield color effects as a result of the periodic arrangement of the mono-dispersed particles therein. Specifically, a plurality of mono-dispersed particles is assembled in a closely-packed and regularly-ordered structure to form one photonic crystal microsphere. This highly organized structure, with the size of the mono-dispersed particles in the range of wavelength of visible light, selectively diffracts certain wavelengths and therefore renders a color corresponding to the diffracted wavelengths. The color effects can be optimized by adjusting the refractive index in the structure, changing materials or particle sizes of the mono-dispersed particles, etc.
It is also known to use the photonic crystal microsphere with color effects as a color pigment for preparing various products, e.g., paint, ink, plastic. However, such usage as a color pigment, poses challenges to the photonic crystal microspheres, particularly to the strength of the structure thereof. Without attaining a certain level of mechanical strength, the periodic structure formed by the mono-dispersed particles can be easily damaged (e.g., fall apart), particularly when subjected to a force, for example, in a typical mixing process. With structure damage, the photonic crystal microsphere cannot reliably deliver a desirable color effect.
One reported approach to increase mechanical strength includes the addition of secondary, smaller particles into the spaces between the mono-dispersed particles as a binding agent to hold the microsphere structure together. However, this approach fails to sufficiently consider the ability of these secondary, smaller particles to effectively disperse within the spaces (i.e., minimizing voids). Poor dispersion of the secondary, smaller particles may not significantly improve structure strength, and even in some cases worsen the structure strength.
Thus, there is a need for a photonic crystal microsphere that has a structure of enhanced strength and that maintains a desired color effect (e.g., keeping predetermined color fidelity).
It is an advantage of the present invention to provide a photonic crystal microsphere that enables a pure color (i.e., within a defined wavelength) across the full visible spectrum, without angle-dependency.
It is yet another advantage of the present invention to provide an efficient large scale production method of making a photonic crystal microspheres and/or photonic crystal pigments and/or photonic crystal pigments containing the same.
It is even yet another advantage of the present invention to provide a photonic crystal pigment with improved mechanical strength to various products that otherwise may not be able to because of the mechanical stresses typically associated with the manufacturing processes of the products.